Split Ring Having a Self-Regulating Throttle Gap

ABSTRACT

A self-regulating sealing element for a throttle gap between a rotating and a stationary components is provided. The sealing element includes a split ring located in the throttle gap between the rotating component and the housing and preferably configured as a U-shaped element that both axially overlaps a portion of the stationary housing at the throttle gap and provides an annular space between the split ring and the stationary housing. The split ring&#39;s axial overlapping regions provide a labyrinth seal effect, while the medium in the annular gap provides a self-regulating damper to accommodate eccentricities between the rotating and stationary components. The split ring may be a bi-metal split ring that is configured such that when at operating temperature the axially-overlapping portions of the ring generally conform to the axial faces of the stationary member portion at the throttle gap to further minimize medium leakage across the split ring.

This application is a National Stage of PCT International Application No. PCT/EP2013/069243, filed Sep. 17, 2013, which claims priority under 35 U.S.C. §119 from German Patent Application No. 10 2012 218 606.9, filed Oct. 12, 2012, the entire disclosures of which are herein expressly incorporated by reference.

The invention relates to a split ring for a hydrodynamic throttle gap of a flow machine for fluid pumped mediums, in particular for the throttle gap on the impeller of a centrifugal pump.

Throttle gaps constructed as a split ring, for instance for centrifugal pumps, are known in a variety of versions. They seal the gap between a rotating rotor part, for instance a centrifugal pump impeller, and a fixed stator, for instance a housing. Due to the necessary tolerances in the manufacture of the individual components, there is a minimal gap width which specifically prevents the touching of parts and the formation of friction and wear. In order to reduce the losses at said gap, there are different versions of a gap seal, which however, according to the nature of the pumped medium, are subjected to greater or lesser wear. In this context, a distinction can be made between axial and radial versions. In axially displaceable components, an appropriate axial sealing gap can be realized only with considerable wear.

U.S. Pat. No. 1,037,243 A shows a gap seal, which is composed of elements connected in part to the housing and in part to the rotating part. This labyrinth structure presupposes as a condition a minimal axial displacement of the rotor and, furthermore, exhibits high level of wear and is very complex in terms of the installation and axial adjustment of the rotor. Where an axial displaceability of the rotor is demanded, a radial sealing gap, which implies low wear, high operating reliability and simple installation, yet implies a high loss coefficient and a lower hydraulic efficiency, is used. Here the hydraulic efficiency through the throttle gap stands in reciprocal relationship to the wear and operating reliability, the higher the efficiency, the higher the wear and the lower the operating reliability.

EP 0905381 A1 shows an embodiment of a split ring in a flow machine, in which both high hydraulic efficiency and high operating reliability is ensured by low wear. EP 0905381 A1 concerns the static part of a hydrodynamic throttle having self-regulating temperature-dependent damping characteristics in the throttle gap. The throttle gap is constructed as a radial split ring and has displaceability in the radial direction in the gap. This embodiment is usable for any other flow machine having fluid pumped mediums.

U.S. Pat. No. 1,037,243 A shows a gap seal which can be composed of one or more elements forming part of the stator.

The object of the invention consists in providing a sealing element which minimizes the gap between the rotor and stator of a centrifugal pump and which autonomously dynamically regulates said gap to a minimum, whereupon the wear is minimized and high operating reliability is ensured.

The object is achieved by virtue of the fact that, on that surface of the stator, for example the housing, which radially delimits the gap, a radial annular space filled with medium is formed or enclosed by the split ring that is present. This radial annular space acts as a buffer and is oriented such that it is centered radially in the direction of the rotating component.

The enclosure of the defined space is realized by the split ring of U-shaped configuration, the U-shaped split ring being guided by a fit of the inner side of the legs of the U in the stator, wherein this fit is set on a temperature-dependent basis by a specific choice of material of the legs and, at operating temperature, the least distance apart or the narrowest fit clearance is realized. This axial gap from the static split ring to the stator is thus kept very small.

The U-shaped split ring forms together with the medium buffer a labyrinth-like seal. The position of the split ring is influenced by the rotating component. Since the split ring is floatingly mounted, it can automatically center itself, given a slightly eccentric position due to different pressure relationships, into a position corresponding to a balanced force relationship. The gap between the static split ring and the rotating component is minimized, wherein the throttle remains constantly free from contact.

The working method of the split ring is based on the working method of two dynamically crafted regions. The first region is the traditional throttle section of a radial gap, wherein, as a result of the hydraulic effects in the rotatory gap, stabilization is produced by the centering radial force as a function of the gap width. The second region is filled with resting medium in the buffer, which is statically sealed by the split ring geometry. The medium which is contained there can flow locally through the throttle section between the legs of the U-shaped split ring and the housing when the split ring is deflected by an eccentricity of the rotor or a deflection, as described in the paragraph above. Upon local displacement of the medium in the buffer, the medium is automatically fed back out of the surrounding flow space, whereby the buffer always contains the same volume. The annular space buffer filled with medium thus possesses a damping characteristic, since a specific pressure must act on the medium in order for this to be displaced through the axial gaps of the gap legs. This pressure, and thus also the damping characteristics, are set by the fit and choice of material of the described split ring in accordance with the operational requirements. A further advantage of this design is the lubricating effect of the flowing medium in the throttle section on the gap legs, whereby the friction during the centering operation of the split ring during layout is minimized to a fraction of the normal friction coefficient from metal to metal, and thus a jamming of the legs on the stator is thus almost impossible as a result of the medium lubrication and a constant, operationally reliable self-centering of the split ring relative to the rotor is ensured.

In an advantageous embodiment of the invention, it is provided in respect of the sealing element that the fit of the axial throttle gap is adjustable. As already described, the split ring can move freely in the radial gap in accordance with the acting restoring forces. The damping characteristics are set by the axial two-sided throttle section of the split ring on the stator. As a result of the pressure difference between before and after the split ring, a flow through the axial gaps in the direction of the low pressure space will become established, whereupon the annular space is supplied with medium and pressurized. The medium enclosed in the gap acts as a hydrostatic buffer. Upon displacement of the rotor, the medium in the gap is forced through the throttle gaps of the split ring into the flow space of the pump. The narrower the gap, the higher the necessary force for surmounting the throttle gap, the higher the hydrostatic damping effect in the gap. The adjustment of the axial throttle gap regulates the hydrostatic damping effect.

In a further embodiment, the sealing element is made of at least one metallic material. In this case, the desired convex deformation of the split ring for the described throttling effect can be obtained by appropriate geometric alteration, such as, for instance, wall thickness differences or stress notches.

Alternatively, the split ring is constructed as a bimetal split ring, wherein the inner layer, i.e. the layer facing the stationary housing, has a substantially smaller thermal expansion coefficient than the outer layer facing the flow space.

Both embodiments realize a heat-dependent throttling effect and heat-dependent rotor damping. If the side flanks of the gap deform convexly outward in the event of heat input and narrow the gap in the direction of the stator component, then the hydrostatic damping of the rotor is increased.

In a further embodiment, the sealing element consists of one or more elements, which are positively pressed or screwed onto the stator geometry. For the possibility of radial deflection, a corresponding free annular space is provided outside the split ring, the radial extent being governed by the magnitude of the anticipated deflection of the rotor.

In a further embodiment, an anti-rotation mechanism, for instance consisting of a slot and a pin, is additionally provided. As a result, an unwanted relative movement between the split ring and the stationary stator housing is additionally precluded. The mobility in the concentric direction is herein maintained.

Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of one or more preferred embodiments when considered in conjunction with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a first embodiment of a sealing arrangement according to the invention, and

FIG. 2 shows a second embodiment of a sealing arrangement according to the invention.

DETAILED DESCRIPTION

In FIG. 1 a first embodiment of the inventive sealing arrangement of a split ring is represented in detail, wherein, in the example, a centrifugal pump is used. A centrifugal pump impeller 1, which in this arrangement is the rotating rotor component, rotates in relation to a housing 2 and a diffuser 3, which can be regarded as stationary in the form of a stator.

According to the invention, the gap is intended to be closed by a U-shaped unipart or multipart cylindrical split ring 7. The split ring is disposed above the throttle diameter or gap diameter 6 of the centrifugal pump impeller 1 in the stator consisting of the housing 2 and the diffuser 3. The split ring, via the legs 7 and 10 or 12 and 13 of a U-shape for guidance, is fitted appropriately in the housing.

The split ring 7 realizes two radial functional gaps, the existing radial throttle diameter or gap diameter 6 of the centrifugal pump impeller as a constantly flowed-through gap and the enclosed quasi-static annular gap space 4 within the described U-split ring construction. In the axial direction an axial gap 5 is present, which enables mobility of the split ring 7 in the housing 2 and/or on the diffuser 3.

Due to a pressure difference, a low quantity of the pumped medium is moved continuously through the gaps 4 and 5, whereby an adequate lubrication of the surfaces is given. A first variant of the split ring 7 according to the invention is composed in the centrifugal pump of a plurality of parts, wherein, in the example of FIG. 1, a possibly profiled, flat ring is connected by a fastening 8 to a ring profiled in an L-shape. This fastening 8 can be formed, for instance, by one or more additional components, for instance a screw joint, or by a weld, in particular produced by a laser welding process. Due to the gaps which are present, the composed split ring is movable in the radial direction, wherein the maximum deflection is defined by the radial clearance 9.

Depending on the field of application, it can be advantageous if the split ring 7 can move completely freely. In particular, the possibility thus exists to reduce velocity-dependent and distance-dependent friction forces. For many applications, it becomes advantageous, however, if the split ring 7 is secured in its position. For this purpose, in the split ring can be provided a radially oriented slot, in which a pin, connected, for instance, to the housing, engages. This anti-rotation mechanism 10 is represented in FIG. 1 only schematically.

FIG. 2 shows a further embodiment of a split ring 7 according to the invention, wherein this is made of a circumferentially closed bimetal strip 11 pressed into the stator. As is already shown in the above example, the split ring 7 is a fixed constituent part of the stationary component.

In the embodiment as a bimetal split ring is used a 2-layered material, the inner layer 11 of which has a substantially smaller expansion coefficient than the outer layer 12. The side flanks of the gap deform convexly outward in the event of heat input and narrow the gap 5 to the stator component, whereby the hydrostatic damping of the rotating component is increased. The bimetal construction realizes a heat-dependent throttling effect and heat-dependent rotor damping. The heat-dependent throttling effect and heat-dependent rotor damping can also be achieved by purposeful influence on the geometry of a monosteel split ring. The multipart and unipart construction can be made respectively of monosteel and bimetal.

In general terms, this arrangement dictates that the split ring 7, in the installed state, is freely movable between the clearance 6 to the stationary housing 2 and the rotating component 1. The split ring 7 rests at standstill in an end position on the rotating component. When the radial gap 6 is axially flowed through with medium by the rotation of the rotating component 1, the split ring 7 centers itself, due to the actual Lomakin effect, relative to the rotating component 1, and a centric clearance appears between the split ring 7 and the rotating component 1. If the rotating component 1 is radially deflected by non-steady or steady operating states, the split ring 7 yields dynamically in this region, whereupon the gap 6 between the impeller 1 and the split ring 7 is lessened, resulting in an increase in gap flow velocity in this region. This velocity increase in the gap 6 generates, in opposite direction to the deflection force, a counterforce in the gap 6, until the impeller 1 is again flowed through centrically to the split ring 7 or a uniform radial nominal clearance to the rotating component 1 is achieved.

As a result of this dynamic self-regulation, no rubbing or jamming of the rotor with the stator is possible in this region.

The damping characteristics are set by the axial two-sided throttle section 5 of the split ring 7 on the projection. As a result of the pressure difference between before and after the split ring 7, a flow through the axial gaps 5 in the direction of the low pressure will become established, whereupon the gap 4 is supplied with medium and pressurized. The medium enclosed in the gap 4 acts as a hydrostatic buffer. Upon displacement of the rotor, the medium in the gap 4 is forced through the throttle gaps 5 of the split ring 7 into the flow space of the pump. The narrower the gap 5 is, the higher is the necessary force which is required to surmount the throttle gap 5 and, at the same time, this corresponds to a higher hydrostatic damping effect in the gap 4. The hydrostatic damping effect is set by the fit of the axial throttle gap 5.

The leakage flow which is formed by the displacement of the medium in the radial gap 5 upon deflection of the impeller 1 minimizes the friction between the moved (upon deflection of the impeller) and the stationary components, in particular the housing 2 and the diffuser 3. As a result of the throttle gap 5, the wear of the stationary components at the assumed points of contact is markedly reduced, which additionally increases the operating reliability.

All variants of this dynamic, movable split ring 7 can be provided with appropriate flow profiles in the gap 6, so that a still smaller gap and better efficiency of the centrifugal pump can be achieved.

The foregoing disclosure has been set forth merely to illustrate the invention and is not intended to be limiting. Since modifications of the disclosed embodiments incorporating the spirit and substance of the invention may occur to persons skilled in the art, the invention should be construed to include everything within the scope of the appended claims and equivalents thereof.

REFERENCE SYMBOL LIST

-   -   1. impeller     -   2. housing     -   3. diffuser     -   4. gap     -   5. axial gap     -   6. radial gap     -   7. split ring     -   8. fastening     -   9. radial clearance     -   10. anti-rotation mechanism     -   11. bimetal plate     -   12. inner layer     -   13. outer layer 

1-6. (canceled)
 7. A sealing element for sealing a throttle gap between a rotating component against a stationary housing, comprising: a split ring configured to seal the throttle gap between the rotating component and the housing, wherein the split ring is sized such that an enclosed annular space exists between the split ring and a portion of the stationary housing delimiting a radially outer extent of the throttle gap when the split ring is in an installed position on the stationary housing; the annular space is concentric with the rotating component at a location on the rotating component delimiting a radially inner extent of the throttle gap; the split ring has a U-shaped configuration around the annular space, with ends of the U-shape overlapping axial faces of the portion of the stationary housing delimiting the radially outer extent of the throttle gap such that at least one axial gap is formed between the U-shaped split ring and the portion of the stationary housing delimiting the radially outer extent of the throttle gap.
 8. The sealing element as claimed in claim 7, wherein a fit of the split ring in the axial throttle gap is adjustable.
 9. The sealing element as claimed in claim 7, wherein the split ring is made of at least one metallic material.
 10. The sealing element as claimed in claim 9, wherein the split ring is a bimetal split ring, the bimetal split ring is a one piece pressed split ring or a multipart split ring, and an inner metal layer of the bimetal split ring has a substantially smaller thermal expansion coefficient than an outer layer of the bimetal split ring.
 11. The sealing element as claimed in claim 9, wherein the split ring is constructed as a sheet metal profile, and the sheet metal profile split ring is a one-piece pressed split ring or a multipart split ring.
 12. The sealing element as claimed in claim 7, wherein the split ring includes at least one of a slot and a pin configured to cooperate with at least one corresponding feature of the stationary housing to suppress rotation of the split ring relative to the stationary housing. 